JPS63111128A - Manufacture of high tension high carbon steel wire rod having superior drawability - Google Patents

Abstract

PURPOSE:To prevent cup fracture due to central segregation and to improve the strength and ductility by adding a specified amt. of V to a steel having a specified compsn. contg. regulated amts. of Cr and Si and capable of being cold drawn without reheating. CONSTITUTION:A steel consisting of, by weight, 0.5-0.9% C, 0.3-0.6% Si, 0.4-0.9% Mn, 0.02-0.20% V, 0.03-0.10% Cr and the balance Fe is hot rolled to a wire rod and this wire rod is coiled in the form of a ring and subjected to direct controlled cooling by blast. Even when lead patenting by reheating is omitted, the wire rod can be drawn and cup fracture is not caused during drawing. In the steel, V has a strength and ductility improving effect but <0.02% V does not produce the effect. In case of >0.20% V, the effect is not further enhanced and the cost is increased, so the amt. of V in the steel is restricted to 0.02-0.20%.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing a high-strength, high-carbon steel wire rod with excellent wire drawability, and in particular allows cold wire drawing without reheating treatment. This method is used in the field of manufacturing high-strength m-wire such as PC steel stranded wire.

[Conventional technology]

Conventionally, in order to manufacture high-strength steel wires such as JIS G3536 PC steel wire and PC steel stranded wire and JIS G3521 hard steel wire, high carbon steel wire rods are hot-rolled and then lead patented to improve wire drawability. In order to obtain a good sorbite structure, a method was adopted that also satisfied the required characteristics of the final product.

However, in recent years, lead patenting has been omitted,
A method of obtaining a final product by wire-drawing as-rolled material that has been directly adjusted and cooled has come to be used. However, there is an increasing demand for increased strength in the final product.

Therefore, the properties of the material directly affect the strength and ductility of the final product, the life of the die during the wire drawing process, and the wire drawability itself. For example, in the case of PCfi stranded wire, the degree of wire drawing is approximately 85%, the final diameter is 3 to 5 mm, and the material diameter is generally a large diameter size of about 8 inches or more.

Generally speaking, countermeasures such as setting the winding temperature, which is one of the factors for improving strength, to a higher value are taken because "insufficient strength tends to occur during blast-controlled cooling," but in this case, The thicker the secondary scale becomes, the more likely it is to fall off, and by the time it is used by a consumer, it will partially develop red rust and will not peel off even when pickled before wire drawing, reducing the life of the die.

On the other hand, when cold wire drawing is performed without lead patenting, it is well known that center segregation of the material is a major factor that inhibits its workability. Annealing is performed, but the heat treatment cost is enormous. Further, the amount of C or Mn may be increased for the purpose of increasing the strength, but since these elements are segregated elements, this becomes increasingly disadvantageous in terms of center segregation.

In addition, the present inventors previously disclosed Japanese Patent Application Laid-Open No. 60-2631.
A method of omitting lead patenting by adjusting the chemical composition has been proposed, as seen in
However, the above-mentioned problems have not been comprehensively pursued, and there are limits to how much strength and ductility can be improved by this method.

[Problem that the invention seeks to solve]

An object of the present invention is to solve the above-mentioned problems of the prior art, to provide a method for manufacturing a wire rod for high-strength steel wire, which prevents cuppy fracture due to center segregation, and which allows wire drawing processing as it is rolled. .

[Means and operations for solving the problems] The gist of the present invention is as follows.

That is, in terms of weight ratio, C: 0.5-0.9% Si: 0.3-0.6% Mn: 0.4-0.9% V: 0.02-0.20% Cr: 0. 03 to 0.10%, with the balance consisting of Fe and unavoidable impurities, is hot-rolled into a wire rod, then wound into a ring shape and directly blast-controlled and cooled. This is a method for producing high-tensile, high-carbon steel wire with excellent wire workability.

First, each added element is adjusted as follows.

C: C is an element that has a large effect on the strength and ductility after hot rolling or wire drawing, and the upper limit is 0.9%.
shall be. The reason for this is that if this value is exceeded, the degree of center segregation deteriorates significantly, and furthermore, pro-eutectoid cementite with low plasticity precipitates, which significantly impedes wire drawability.

On the other hand, if it is less than 0.5%, the amount of pro-eutectoid ferrite will inevitably increase and the required strength will not be obtained, so the lower limit is set to 0.5%.
%, and was limited to a range of 05 to 0.9%.

Sl: Si is an element that aims at solid solution strengthening of the matrix and contributes to improving strength, ductility, and relaxation properties, and was limited to a range of 0.3 to 0.6%.

The reason for this limitation is the hard steel wire 5WRH, 7 with a different amount of Si.
2A, when the relaxation characteristics were adjusted for a material with a diameter of 5.5 mm and a processing degree of 80%, the first
As shown in the figure, the relaxation properties are rapidly improved when the content exceeds 0.3%, and the effect is saturated when the content reaches 0.6%, so there is no need to add more than this.

Mn: Mn must also be added in an amount of 0.4% or more to ensure strength. However, if it exceeds 0.9%, the degree of center segregation deteriorates, and at the same time, a martensitic structure is generated during conditioning cooling, which greatly impedes wire drawability, so it is limited to 0.9% or less.

V: ■ is a carbonitride-forming element, and its precipitation-strengthening effect is well known mainly for medium- and low-carbon steels, but as a result of various studies, it was found that it can be applied to high-carbon steels. death,
It has the effect of improving strength and ductility. However, 0,02
If it is less than 0.0%, there is no effect, and if it exceeds 0.20%, the effect will be saturated and the cost will increase, so 0.02 to 0.20%.
limited to the range of

Cr: Cr is an element that improves hardenability and contributes to increasing strength, but
On the other hand, it also has the property of solidifying the secondary scale after rolling the wire rod. Crf! 5WRH72A with k varied in the range of 0.01 to 0.10% was rolled under normal conditions, and after adjusting and cooling, the falling off of secondary scale was observed from the appearance of the coil. As shown in Fig. 2, Cr was 0.1%. Since there was no dropout at 0.03% or more, the lower limit of Cr was set at 0.03%. On the other hand, the upper limit is 0.10% considering fine adjustment of strength.
And so.

In the present invention, after rolling the high carbon steel with the above-mentioned limited components into a wire rod,
It is wound into a ring shape and cooled by direct blast control.
The heating, rolling, and adjusted cooling conditions need not be particularly limited and may be carried out under commonly used conditions. Thus, the wire produced by the method of the present invention can be subjected to cold wire drawing without being subjected to reheating treatment.

〔Example〕

This will be explained in more detail based on specific examples.

The test steel whose chemical composition is shown in Table 1 was made into steel slabs with a body angle of 150 mm, and heated to 1150°C.
It was rolled to 0 mm. 214 degrees for wire finishing is approximately 1050 degrees
~1000℃, and immediately after finishing using a water cooling zone 88
It was rapidly cooled to 0-900°C and subjected to direct controlled cooling in a winding Stelmor cooling device.

The mechanical properties and microstructure of the as-rolled wire were investigated and the results are shown in Table 2. The characteristic values of the microstructure are expressed as pearlite lamella spacing measured with a scanning electron microscope at 3000 times magnification. The smaller this value is, the better the wire drawability is.

Compared to the strength and reduction of area of comparative fiA1, A2, and A3, the steels of the present invention all exhibit higher values, and the pearlite lamella spacing, which is a microstructural factor, is finer. Further, the steel of the present invention has no secondary scale falling off.

Compared to comparative steels A1 and A2, inventive steel B or C,
D has a strength increase of approximately 8 kg f 7 mm2, Si, C
The effects of r and V are obvious. In addition, the steels E, F, and G of the present invention exhibit similar effects compared to comparative steel A3. In general, increasing strength and increasing diameter deteriorate ductility, but as shown in Table 2, the steel of the present invention is superior to comparative steels, and this is due to the reduction in the pearlite lamella spacing. Furthermore, although some pro-eutectoid cementite was observed in the segregated areas in comparison fiA3, where the influence of center segregation is likely to become apparent, it was not detected in the invention steels F and G, suggesting that they have good workability.

Next, the properties after wire drawing will be explained. The wire rods shown in Table 2 were examined for wire drawability using a continuous wire drawing machine.

In other words, the tensile test value at the final wire diameter, die life, and presence or absence of wire breakage during wire drawing were investigated, and the results were used in the third
Shown in the table. As a pretreatment, a pickling-borax treatment was performed to give a total area reduction rate of about 83%, and the final wire drawing speed was about 350 m/min.

Table 3 Comparison Compared to fiA1, A2, and A3, the corresponding steels of the present invention retain the as-rolled properties, are clearly higher in strength and reduction of area, and have good die life. Also, the recognized comparison of pro-eutectoid cementite #4A3
F of the steel of the present invention caused cuppy wire breakage during wire drawing.
, G caused no trouble at all. Furthermore, the length is 300 m+
Fifty specimens of ++ specimens were consecutively sampled and subjected to a tensile test to investigate the incidence of cuppy fracture surfaces, and the results are shown in Table 4. The cuppy fracture surface ratio was determined by the following formula.

The cuppy fracture rate is as shown in Table 4 (in the comparative steels, the rate increases as the C or Mn content increases, but in the steel of the present invention, no cuppy fractures occur at all even when the C1Mn content increases). .

Furthermore, after bluing, a JIS G3536 Nyorori luxation test was conducted, and the results are also shown in Table 4, and it is clear that the steel of the present invention has a sufficiently lower value than the comparative steel, and is superior. .

〔Effect of the invention〕

As is clear from the above examples, the present invention is based on a specific relationship in which Si, Or, and V are added in small amounts in consideration of strength and ductility after wire drawing, wire breakage problems during processing, die life, etc. By adjusting this, it is possible to draw the wire without breaking the wire even if the lead patenting treatment by reheating is omitted, and it is possible to produce a high-strength blue wire that fully satisfies the desired properties, making it possible to produce a high-strength blue wire that fully satisfies the desired properties. This greatly contributes to reducing manufacturing costs for wires, etc.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the Si content and the luxation value, and FIG. 2 is a diagram showing the relationship between the Cr content and the incidence of secondary scale shedding.

Claims (1)

[Claims] (1) Weight ratio: C: 0.5-0.9% Si: 0.3-0.6% Mn: 0.4-0.9% V: 0.02-0.20% Cr: 0 .03 to 0.10%, with the balance consisting of Fe and unavoidable impurities, is hot-rolled into a wire rod, then wound into a ring shape, and directly blast-controlled and cooled, without any reheating treatment. A method for manufacturing high-tensile, high-carbon steel wire with excellent wire drawability.